1. Technical Field
The present invention concerns a heat-resistant alloy having good strength and anti-corrosion properties at high temperature. The alloy of this invention is suitable as the material for skid rails of furnaces used in, for example, steel industry for heating steel pieces.
2. Prior Art
Steel plates and steel wires are produced by rolling the steel pieces called slabs or billets after uniformly heating them in a heating furnace such as walking beam furnace or pusher furnace. If the temperature of the steel piece is lower at the position where the steel piece contacts the furnace bed than at the remaining positions, then uneven thickness of the rolled steel plate or even cracking may occur. In order to avoid these troubles, it is necessary to raise the temperature of the furnace bed at the position of contact with the heated piece to the temperature near the heating temperature. Thus, at the highest temperatures of use the furnace bed metal attains a temperature as high as 1300.degree. C. or more.
As a typical material for the furnace bed withstanding a high temperature of 1150.degree. C. or higher, there has been used a solid solution strengthened type heat-resistant casting alloy, which contains, in addition to Fe, 20-35% Cr, 15-35% Ni and 5-50% Co as the main components, and 0.5-5% Mo, 0.5-5% W and 0.2-4.0% Ta as the solid solution strengthening elements. However, skid rails in the soaking zone of a furnace are subjected to a high temperature such as 1200.degree.-1350.degree. C., and suffer from heavy strain and abrasion. The above mentioned conventional heat-resistant casting alloy of the solid solution strengthened type is not satisfactory as the material of the skid rails.
It has been proposed to use ceramics having high heat-resistance and anti-abrasion properties as the material of the furnace bed metal (for example, Japanese Utility Model Publication No. 35326/1989). So-called fine ceramics materials such as SiC and Si.sub.3 N.sub.4 preferable from the viewpoint of high shock-resistance, which is one of the properties required for skid rails, are easily damaged by oxidation when used in a strongly oxidative atmosphere.
On the other hand, super alloys of the oxidedispersion strengthened type, i.e., Ni-based super alloys in which fine particles of an oxide having a high melting point such as Y.sub.2 O.sub.3 are dispersed, find application in gas-turbines and jet-engines (for example, Japanese Patent Publication No. 38665/1981). As to high temperature furnaces it has been proposed to use an oxide-dispersion strengthened type super alloy of the composition consisting of 12.5-20% Cr, up to 1% Al, up to 0.1% C and up to 0.5% (volume) Y.sub.2 O.sub.3, the balance being Ni, as the material for mesh belts (Japanese Patent Publication No. 9610/1984).
One of the assignees attempted to use the oxide-dispersion strengthened type super alloys as the material of the skid member of a skid rail, and as the result of research, it was discovered that an oxide-dispersion strengthened type super alloy consisting of 18-40% Cr, up to 5% Ti, the balance being substantially Ni, and containing 0.1-2% of fine particles of a high melting point metal oxide dispersed in the austenite matrix thereof is useful as the material for the skid rail. The discovery has been disclosed (Japanese Patent Application No. 14044/1989).
In the furnaces using heavy oil as the fuel, however, Ni-based super alloys are easily corroded due to high temperature sulfidation attack by the sulfur in the heavy oil. The material having sufficient anti-corrosive properties is, for example, Fe--Ni--Cr--Co--W solid solution strengthened heat resistant cast alloy. If oxide-dispersion strengthened heat resistant alloy having the matrix composition similar thereto is obtained, then the alloy will be a material suitable for the furnace bed metal without the above drawback.
Needless to say, Ni-based alloys are expensive, and therefore, it is desirable to construct the skid rails with a less expensive alloy.